Lithographic plate preparation



Patented Aug. 31, 1943 UNITED 1a LITHOGRAPHIOPLATE PREPARATION William H. Wood, Bedi'ord, Ohio, assignor to Harris-Seybold-Potter Ohio, a corporation of Ohio No Drawing. Application April 13. 1940,-

In the manufacture of deep-etch lithographic plates it is customaryto coat a cleaned and counter-etched zinc or aluminum plate with a "resist" which is sensitive to light, and the plate is then exposed to light in the form of the subject matter which is to be reproduced, such that in those areas whereno image is desired on the finished plate the resist is hardened; then theunhardened areas of the resist are removed by a developing.

agent so asto leave the image portions of the plate clean. A so-called deep-etching solution.

is then applied to the plate and allowed to attack the exposed image areas until the metal is etched away to the desired depth, andafter drying, the deep etched areas are treated with material, commonly referred'toas a lacquer, to render them receptive to ink. Subsequently the light-hardened areas of the resist, which during etching have served toprotectthe non-image areas of the plate, areremoved by a clean-upi solution. The plate is then given a desensitizing etch to make the non-imageareas receptive to. water'and is ready for printing. In accordance with the present invention, improved procedure and materials are involved, such as to afford'more easy manipulation and control, and more reliable and positive action, and making possible the production of plates having improved longevity, definition, fidelity and uniformity. i

To theaccomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, and particularly pointed out ,i'n the claims, the following description settlngforth in detail certain illustrative embodiments of theinvention, these bein indicative however, of but a few of the various ways in whichthe principle of the invention ma be employed. V I n i In the preparation of plates in accordance with my invention, I apply a combination of a waterfsoluble colloid coating material together with a material providing arabic acid.

Illustrative of the water-soluble colloids are albumen, coldwater soluble gelatin, polyvinyl alcohol, dextrine, methyl-cellulose, etc. The action of arable acid with these is to toughen them, thereby forming a I improved contrast between exposed and unex- Serial No. 329,56 7 1': Claims. (01. 95-41) Company, Cleveland...

posed areas on the final plate, as compared with other bases. The arabic acid action in touzhen-= ing, and the salt action in raising the solubility,

afford thus two variable controls by which the I amount of solubility and the amount of toughening respectively, maybe directed as preferredin any given instance. Arabic acid is prepared by adding anhydrous alcohol to a solution ofhydrochloric acid and gum arabic. Arabic. acid is formed as a precipitate; This precipitate. is washed several times with anhydrous alcohol,

, filtered and dried. It is then dissolved in water to form a solution of desired concentration, for example twenty per cent, and this solution is neutralized accurately with ammonium hydroxidepforming ammonium arabate. In using.

a pH meter, a pH of seven isdesirable. The arabic acid compound is now combined with the water-soluble. colloid, and for example this may involveone-part of a. twenty per cent wate'rsolution of egg albumenand four parts of a twenty per cent water solution of'ammonium arabate. Whilethese proportions are particularly desirable, up to equal amounts of the two solutions may advantageouslybe used. i

, Such combination material ior coating, suitably sensitized with a soluble dichromate or the like as usual, is coated onto the metalplate, as by the usual means. This coating or resistant material gives certain notable new results and advantages: (1) it flows more readily and uniformly than the known gum .or gum-glue solutions; '(2) it forms a very thin coating while preserving its protective quality and thus minimizes the distortion of tone values which in known resists results fromthe spreading of the light during exposure; (3) the exposure required 'is relativel un-influenced by the humidity of the surrounding air and in this respect is very much less effected than is the case with the usual resists; (4) it has spe--' cial receptivity to action by'fthedeveloper materials described hereinafter, in those areas which are unhardened by light, thus making possible an improved developing action over that which can be attained withthe usual resists treated with known developers or treated with the new developer materials.

I The coated metal plate (the metal beingusual or as preferred, zinc, aluminum, etc.), having been exposed to light and the subject matter which is to be reproduced, is treated with the developer; Any developer as customary in the art may be employed, or preferably that in accordance with my patent aplication Serial No. 223,523, as this in conjunction with the present coating gives outstanding advantages. This developer involves a solution of magnesium chloride and a hydroxydicarboxylic acid, such as malic acid, or somewhat less desirably tartaric acid. For example there may be 65 to 72' per cent MgClaGHzO and 2.5to per cent of the hydroxydicarboxylic acid.

Following removal of the unhardened portions of the coating or resist by the developer, the plate may be etched in customary or preferred procedure; and the hardened resist is next removed from the non-image areas of the plate which it has protected during the etching, and the plate is finished, as usual.

This application is a continuation, in part, as to common subject matter, ofmy Patent No. 2,265,829, issued December 9, 1941.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the featuresstated inany of the following claims, or

r the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention: q

1. In a process of making lithographic plates,

applying to the plate a surfacing of ammonium arabate and egg albumen in the proportions of one part of a twenty percent solution of albumen to one to four parts of atwenty per cent solution of the arabate, and providing a light-sensitizing agent.

2. Inc. process of making lithographic plates,

applying to the plate a surfacing of ammonium arabate and egg albumen, the proportion of the former in general not exceeding the latter, and at any desired stage providing a light-sensitizing agent. I Y

3. In a process of making lithographic plates, aplying to the plate a surfacing of a water-solu-r ble colloid other than gum arabicv together with ammonium arabate, and at any desired'stage providing a light-sensitizing agent.

4. In a process of making lithographic plates, applying to the plate a surfacing of a watersoluble colloid other than gum arabic together with a material providing an arabic acid radical from the group consisting of arabic acid and salts formed by reacting arabic acid with a base, and at any desired stage providing a light-sensitizing agent.

5. In a process of making lithographic plates, toughening a water-soluble colloid coating other than gum arabic by inclusion of arabic acid, and at any desired stage providing a light-sensitizing agent.

6. In a process of making lithographic plates,

applyingto the plate a surfacing of awater-soluble colloid other than gum arabic and arabic acid with a base which produces a water-soluble salt of arabic acid, and. at any desired stage providing a light-sensitizing agent.

7. In a process of making lithographic plates,

applying to the plate a surfacing of a water-soluble colloid other than gum arabic and arabic acid, and controlling the degree of solubility of the latter by inclusion of a base which produces a water-soluble salt of arabic acid, and at any desiredstag'e providing a light-sensitizing agent.

8. In a process of making lithographic plates, applying to the plate a surfacing of a water-soluble colloid other than gum arabic, and toughening the colloid by inclusion of arabic acid, and

controlling the solubility of the arabic acid by inclusion of a base which produces a water-soluble salt of arabic acid, and at any desired stage providing a light-sensitizing agent.

9. In a process of making lithographic plates,

applying to the plate a surfacing of a water-soluble colloid other than gum arabic and arabic acid, and subsequently treating the surface with a solution of magnesium chlorideand 'malic acid,

and at any desired stage providing a light-sensitizing agent.

10. In a process of making lithographic plates,

applying to the plate a surfacing of a water-soluble colloid other than gum arabic and arabic acid,

and subsequently treating the surface with a solution of magnesium chloride and a hydroxydicarboxylic acid, and at any desiredstage providing a light-sensitizing agent.

11. A lithographic plate surfaced with ammonium arabate and egg albumen, and at any desired stage provided with a light-sensitizing agent. I

. 12. A lithographic plate surfaced with the products of arabic acid and a water-soluble col-- loid other than gum arabic, and at any desired stage provided with alight-sensitizing agent.

13. A lithographic plate surfaced with ammonium arabate and a water-soluble colloid other than gum arabic, and at any desired stage provided witha light-sensitizing agent.

14. A lithographic plate surfaced with a watersoluble colloid other, than gum arabic and a material providing an arabic acid radical from the group consisting of arabic acid and salts,

formed by reacting arabic acid with a base, and at any desired stage provided with a light-sensitizing agent.' 7

. 15. A lithographic plate surfaced with a watersoluble colloid other than gum arabic, and arabic acid and a salt of arabic acid, and at any desired stage provided with a light-sensitizing agent.

16. In a process of making lithographic plates, applying to the plate an ammonia-neutralized aqueous solution of a precipitate from addition of alcohol to a hydrochloric acid solution of gum arabic.

17. A lithographic plate having a surfaceformed from ammonia-neutralized aqueous solution of a precipitate from addition of alcohol to a hydrochloric acid solution ofgum arabic.

WILLIAM H. WOOD. 

